1. Field of the Invention
This invention relates to the production of sulfolene. Sulfolene, or butadiene sulfone, is a well known cyclic monosulfone which has considerable value as a chemical intermediate (and as a source of pure butadiene by thermal decomposition). It can be readily hydrogenated to sulfolane, which is a valuable selective solvent for many organic substances, as well as a thermally stable inert reaction medium.
2. Description of the Prior Art
The conventional method for preparing sulfolene is to mix a large molar excess of liquid butadiene, or the appropriately substituted diene, with liquid sulfur dioxide under non-aqueous conditions, at pressures between 100 and 500 pounds per square inch and at a temperature of about 100.degree. C. The reaction times required under these conditions, that is, without some modification of the process, can be as high as two days. The bulk of the literature as a consequence, is largely composed of reports on optimizing this basic process.
In addition to the problem of extended reaction times, sulfur dioxide and butadiene in the conventional processes also react to form (insoluble) polymeric butadiene sulfones; generally those conditions which increase the reaction rate for the sulfolene reaction also increase the rate for the polymer reaction.
Because of these factors, most of the investigative work on sulfolene, and conjugated diene sulfones has been oriented toward improving the efficiency and yield from the sulfolene reaction. This has resulted in the development of methods involving the use of polymer inhibitors to prevent formation of the polysulfone (U.S. Pat. No. 2,443,270); sodium hydroxide washing of the butadiene to eliminate peroxides, which favor the formation of polymer (U.S. Pat. No. 2,420,834); and various techniques to achieve improved results by accurately controlling the temperature of the reaction (U.S. Pat. Nos. 2,402,891 and 2,395,050). Other procedures describe the preparation of sulfolene in alcohols or other organic substances (U.S. Pat. No. 3,077,479). German Pat. No. 506,839, dated Sept. 16, 1930 teaches that polyfunctional phenols, which may act as stabilizers for styrene and acrolein, inhibit the formation of polymeric sulfones in a reaction between liquid butadiene and liquid SO.sub.2 or between these reactants in a mutual solvent, such as benzene. This patent does not teach the aqueous dispersion process nor the inhibiting activity of such materials as mercaptans or inorganic salts of lower valence phosphorous acid, such as NaH.sub.2 PO.sub.2.
German Pat. No. 236,386 dated July 4, 1911 discloses the fact that butadiene reacts with sulfurous acid in water to give both a crystalline and an amorphous product. It is significant only in showing that butadiene and aqueous sulfurous acid can react. It does not suggest how to prepare the crystalline product in preference to the amorphous product.
A review of the art shows that, for the most part, no significant work has been directed toward developing a new approach to the actual synthesis of sulfolene.
Accordingly, the fundamental object of this invention is to provide a method of preparing sulfolene compounds in substantially improved yields and in shorter times than can be reached with known methods.